Thermal relay



P 2 G. H. WHITTINGHAM 1,728,092

THERMAL RELAY Filed March 31, 1927 Patented Sept. 10, 1929.

UNITED STATES PATENT OFFICE.

GEORGE E. WHITTINGHAM, OF BALTIMORE, MARYLAND, ASSIGNOR TO MONITOR CONTROLLER COMPANY, OF BALTIMORE, MARYLAND, A. CORPORATION OF MARY- THERMAL RELAY.

LAND.

Application filed March. 31, 1927. Serial N'o. 179,901.,

The purpose of this invention is to provide a simple and inexpensive thermostat switch for opening an electric circuit upon the occurrence of abnormal current conditions in the circuit.

In carrying out the invention, I provide, upon a suitable base, a vertically arranged metal bar which is spaced from the base, and surrounding this bar is a helix of thermally responsive metal, one end of the helix being secured to the bar and the other end projecting laterally with respect thereto. This laterally projecting end forms a switch member which engages an adj ustable switch member mounted on the base. A small resistance coil surrounds the bar and the helix is affected by the heat from this coil, both directly and by conduction from the bar. A stationary contact member, comprising a sheet metal strip, secured to the base, is adjustable toward and from the laterally projecting end of the helix, by an adjusting screw, to cause theswitch to open with more or less current flowing in the resistance coil, as desired, and a dial is provided for indicating the setting of the adjusting screw. The switch, with the features referred to, is self-closing; but where it is desirable to avoid automatic closing of the switch, I provide a simple tripping device which automatically interposes insulating material between the switch contacts when the switch opens, so that the circuit cannot be closed until this device has been manually re-set.

In the accompanying drawing,

Fig. l'is a front elevation of a thermostat switch made in accordance with my invention, the heating coil and the thermally responsive helix being shown in central section;

Fig. 2 is a top plan view of the same; 3

Fig. 3 is a left side elevation of the same;

Fig. 4 is a side elevation of a switch like that shown in the previous figures, but provided with a tripping device which must be manually re-set to close the switch;

Fig. 5 is a top plan view of the same;

Fig. 6 is a side elevation of the tripping device; and v Fig. 7 is a section on the line 7-7 of Fig. 6.

Referring to Figs. 1, 2 and 3 of the drawmg, a indicates a suitable base of insulating material to which the several parts are se-' cured. A sheet metal bracket 6 is secured to the base by a flange l and projects forwardly from the base, and a metal rod or bar 2, secured at one end to the forward end of the bracket extends downwardly therefrom, the bar being spaced from the base by the bracket. A helix 0, composed of layers of metal which expand unequally, surrounds the upper part of the bar 2 and has one of its ends secured to the bar by a set screw 3. The other end a of the helix extends laterally with respect to the bar and constitutes a switch arm which engages a stationary contact member d. The member (5 consists of a strip of resilient sheet metal, bent into U form, as shown in Fig. 3, the arm 5 of the strip extending over the end of the helix, and the arm 6 of the strip being secured to the base by a plate 7, and a stud 8, which extends through one arm of the strip d and through the plate 7, and the base a. A dial plate 10, having circular graduations thereon, is secured to the arm 5 of the strip 03 by a rivet l1 and by the screw 9 which passes throu h the dial and is threaded into the plate 7. n the head of the screw 9 is a pointer 12, for indicating the adjustment of the screw with respect to the graduations on the dial. The end of the arm 5 of the strip at normally bears against the arm 4 of the helix, and it will be evident that by turning the screw 9, the arm 5 may be adjusted so as to vary the pressure of the latter arm against the arm 4. With the heating of helix 0 to a predetermined degree, the time when this arm 14 will leave the stationary contact arm5 will depend upon the adjustment of said arm by the screw 9, and the pointer on the screw will indicate its position of adjustment upon the dial.

A heating coil e surounds the bar 2 and also surrounds the helix. As shown, this coil is mounted upon a spool 13, having at its lower end a sleeve 14, which fits closely around the lower end of the bar 2, and the spool is supported by a cotter pin 15, extending through the lower end of the bar. The spool closes the space below the helix, so that the heat generated in the coil e is retained around the helix.

The coil e is in a circuit 7' in which the cur-- rent may vary, such as the armature circuit of a motor, and in this circuit is arranged a switch 9 which is biased toward open POSI- tion, as by a sprin 16. The switch is nor- 1 mally held in close position by a magnet 17 and thence to conductor 21 leading to the current source. The circuit 72. carries a negligible amount of current which has no appre- -ciable heating efl'ect upon the thermostat.

In the operation of the device shown in Figs. 1, 2 and 3, the thermostat switch remains closed and maintains the electromagnetic switch in the circuit f closed as long as the current in the latter circuit is normal. When the current in the'circuit f rises above a predetermined amount for a short perlod, the heat generated in the coil 0 causes the thermostat helix to uncoil partly and to relax the pressure of the arm 4 against thearm 5 of the contact member d, and to separate entirely from the latter arm and break the circuit .whenthe heat is suflicient. The amount of current in the circuit f required to cause the opening of the thermostat switch depends upon the adjustment of the arm 5 with respect to the arm 4, which adjustment is accomplished by turnin the screw 9. The dial and the pointer on the adjusting screw are an aid to the proper adjustment of the contact members in setting the device. When the circuit is opened by the thermostat, the magnet 17 is de-energized and the switch 9 opens the circuit 7. When the helix 0 cools, it automatically closes the circuit h, and the eleetromagnet then closes the switch f in the circuit f. The device is thus sel -setting;

Figs. 4'and 5, the thermostatic switch is the same as in that shown in the previously described figures, except for the additionof a manual re-setting device, which is shown in detail in Figs. 6 and 7, and of a stop for said re-setting device.

The manual re-setting device In comprises a thin flat piece of insulating material having an opening 22, in which is inserted an eyelet 23 and the ad'ustin screw 9 extends through this eyelet. e e ge of the insulating piece has an arcuate portion 24, concentric wlth the opening 22, and at the ends of this arcuate portion are shoulders 25 and 26, which form stops, co-operating with a fixed stop 7 on the plate 7 to check the movement of the re setting device. Opposite the arcuate edge 24, the insulating piece is shaped to form a handle 27, and above the opening 22 is arranged a contact iece 28, consisting of a small strip of thin sheet metal which is passed through a slit 29 in the insulating material and doubled into U-form against the sides of the sheet so that a metal contact surface is exposed on ea h side of the sheet. An eyelet 30 is provided in the handle portion 27 so that a spring may be attached to the device for operating it from a distance, if desired. The re-setting device is arranged to turn loosely upon the adjusting screw 9, and lies between a contact 31 on the arm 4 and a contact 32 on the arm 5 of the stationary member d, and at normal temperatures it is frictionally held between these contact points.

The operation of the switch shown in Fi s. 4 and 5 is as follows: When the re-setting evice is in the position shown in full lines in Fig. 4, the sheet metal contact 28 lies between and electrically connects the contacts 31 and 32 of the switch members 4 and 5, respectivel and at normal temperatures these mem ers frictionally hold the resetting device in its circuit-closing position. When the helix 0 becomes heated to a predetermined degree, it uncoils and moves the arm 4 away from the opposing switch member 5 and from the re-settingdevice, breaking the circuit, and in this movement the re-setting device becomes released and the weight of its arm 27 causes said device to rock to the dotted line position shown in Fig. 4. In the latter position of the re-setting device, its contact 28 is out of line with the switch contacts and a part of the piece of insulating material then lies between said contacts, so that whcn the helix cools and the switch arm 4 returns to normal position, it cannot close the circuit. To again close the circuit, the operator rocks the resetting device from the dotted line position to the full line position, which movement causes the U-s'haped contact piece 28 to slide in between the contacts 31 and 32 and electrically connect the same. The shoulder 26, engagin the fixed sto 7", limits the movement 0 the re-setting evice in one direction, and the shoulder 25, engaging said stop, limits the movement of said device in the opposite direction.

What I claim is:

1. A thermostat switch comprising a suitable base, a metal bar vertically supported thereon, a helix of thermall responsive metal surrounding the bar an havm one end secured to the bar and the other en proj ecting laterally with respect thereto, a spool surrounding the helix and having a. sleeve at its lower end fitting around and supported on the bar, and aheating coil on said spool.

2. A thermostat switch comprising a suitable base, a metal bar vertically supported thereon, a helix of thermally responsive metal surrounding the bar and having one end secured to the bar and the other end projecting laterally with respect thereto, a sheet metal contact member secured to the base and adapted to bear against said projecting end, an adjusting screw supported on the base and extending through said member and having a pointer, said screw adapted to adjust the position of said contact member with respect to said projecting end, and a dial on said member adjacent the screw.

3. A thermostat switch comprising a suitable base, a metal bar vertically supported thereon, a helix of thermally responsive metal surrounding the bar and having one end secured to the bar and the other end projecting laterally with respect thereto, a Ushaped spring contact member having one arm projecting over said latter end and its other arm secured to the base, and an adjusting screw mounted on the base and extending through said member.

In testimony whereof I hereunto aflix my signature.

GEORGE H. WHITTINGHAM. 

